[Q] No idea how to start an update HELP PLEASE

hello guys im new here and feel stupid to ask this, im not too good with computers and stuff and i really dont know how to start an update my xperia Z to 4.4 kitkat manually, i searched for it but no help because there are many things and versions etc so it got complicated for me, can someone help me? all i know that i got 4.3 update on my xperia Z that is 6603 model

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